Paper filters for coffee extraction are generally available in two color categories: white and yellow-brown. Their coloration is closely associated with whether they undergo a bleaching process. However, beyond the mere change in appearance, bleaching introduces a number of chemical and physical differences that meaningfully influence extraction behavior.
In modern manufacturing, both white and brown filters are produced from the same raw material: the inner portion of wood, after its outer bark has been removed. Brown filters simply omit the bleaching stage, whereas white filters proceed through it. When bleaching is skipped, a substance called lignin remains. Lignin is responsible for the characteristic “woody” odor, and it is highly sensitive to pH changes and oxidation. As lignin oxidizes, both its color and aroma intensify, producing what we perceive as the undesirable “paper smell.” Chemically, lignin is a major structural component of plant cell walls—an aromatic, high-molecular-weight polymer. Functionally, it acts as an adhesive that binds fibers together, provides structural strength, imparts hydrophobicity (preventing the material from readily soaking in water or collapsing), and even serves as a natural antimicrobial barrier.
The bleaching process alters the chemical nature of the filter. Unbleached filters retain trace amounts of lignin, hemicellulose, and microfibers, resulting in a surface that is not fully purified. Such a surface exhibits relatively weaker adsorption, allowing oils and colloidal compounds to pass through more readily. Consequently, brews made with brown filters often present subtly enhanced texture and a slightly elevated perception of sweetness.
Conversely, white filters—having had lignin and residual microfibers thoroughly removed—consist of highly purified cellulose. This purification amplifies cellulose’s hydrophilic character and strengthens its ability to attract and retain oils, colloids, and fine particles. While this may lead to a lighter mouthfeel, it yields a notably cleaner cup. Some people report an increase in perceived sweetness when using brown filters. Sweetness in coffee is influenced primarily by colloids, lipids, high-molecular-weight caramelized carbohydrates, and melanoidins.
These compounds possess high molecular mass and readily adhere to surfaces, meaning that adsorption varies significantly depending on the chemical characteristics of the filter. Because brown filters exhibit lower adsorption capacity, the compounds responsible for sweetness pass through more freely, explaining the enhanced sweetness perceived by some brewers. For these reasons, it is generally recommended to rinse brown filters with hotter water. This step effectively removes odor-active lignin compounds and sufficiently wets the hydrophobic surface before brewing.